Human activities produce large amounts of sulfur-containing residues, which are harmful to the ecology. Thus, the combustion of fossil fuels (coal, oil derivatives), in particular in thermal power plants for electricity production, leads to the formation of a large volume of sulfur oxides, the release of which into the atmosphere is not generally permissible.
One known and recommended technique for purifying flue gases of sulfur oxides consists is treating these gases with sodium bicarbonate. The sulfur oxides from the gas treated are of the type converted to sodium sulfate, easily separable from the gas.
There are various processes for obtaining sodium bicarbonate intended for purifying flue gases.
A first process, generally known as the ammonia process and commonly used in industry, consists in treating an ammoniacal brine with a gas containing carbon dioxide. The sodium bicarbonate obtained containing ammonia residues is calcined and the sodium carbonate obtained is dissolved in water. The resulting solution is recarbonated to produce an aqueous suspension of sodium bicarbonate crystals. The suspension is finally filtered to separate the crystals, which are dried to produce the desired sodium bicarbonate.
Other processes are based on the carbonation of sodium carbonate solutions obtained starting from natural sodium sesquicarbonate (trona).
These known processes have proved to consume large amounts of energy. The sodium bicarbonate that is derived therefrom is relatively expensive. Furthermore, these known processes, in order to be competitive, must be carried out in very large sized plants. The investments necessary for the creation of new plants that meet the present environmental standards are extremely high.
Moreover, these environmental standards require the elimination of sulfur oxides from ever-increasing quantities of industrial flue gases. There is therefore a significant need for sodium bicarbonate for treating flue gases which is inexpensive and of sufficient quality.
The invention aims to solve this problem.